Investigation on Structural Modification of Sri Lankan Vein Graphite for Ion Intercalation
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Date
2015
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Publisher
Uva Wellassa University of Sri Lanka
Abstract
Rechargeable batteries have become the main energy source for the portable electronic devices.
Synthetic graphite have been used as anode electrode material in rechargeable batteries. Presently
these rechargeable batteries are expensive mainly due to high cost of materials, such as synthetic
graphite and metal oxides, used in their electrodes. It is suggested that the cost of these batteries
can be reduce by introducing cheaper natural graphite for their anode electrode. Sri Lankan natural
vein graphite can be classified into four distinct structural verities. They are Shiny-Slippery-
Fibrous Graphite (SSF), Needle-Platy Graphite (NPG), Coarse Striated-Flaky Graphite (CSF) and
Coarse Flakes of Radial Graphite (CFR). Development of Sri Lankan natural vein graphite to the
anode of Li-ion rechargeable batteries, through purification and surface modification have been
investigated recently. Furthermore, natural graphite has to be structurally modified by expanding
interlayer distance to facilitate the intercalation of larger Na ions for the application in
rechargeable Sodium Ion Batteries (SIB) (Wei, 2011). The present study investigated the
possibility of expanding the interlayer distance of Sri Lankan natural vein graphite for
accommodating Na-ion intercalation by converting into Graphite Oxide (GO).
Materials and methods
Purified samples from all four structural varieties of Sri Lankan vein graphite, were used in this
study. Raw graphite samples were oxidized to Graphite Oxide (GO) by using improved hummers
method (Madusanka Y.N., Amareweera T.H.N.G.,Wijayasinghe H.W.M.A.C., 2013). In this
method 96% H2SO4 (Sigma-Aldrich) and 85% H3PO4 (Sigma-Aldrich) were added to purified vein
graphite. Then KMnO4 (Belgolabo) was added little by little to the mixture with in two hours and
stirred. Sample was allowed to cool until room temperature. Solution was poured into 30% H 2O2
in an ice bath and the sample was vacuum filtered using Fisher brand filter papers using distilled
water.
The d.c. electrical conductivity of raw graphite and prepared GO samples were measured using
the standard four probe method. Fourier Transform Infrared (FTIR) spectra of raw graphite and
GO samples were employed to study the structural modification. Further the X-ray diffractometry
was used to confirm the formation of GO.For the Na-ion intercalation study, the modified graphite
oxide was tape casted by the doctor blade method to fabricate electrodes. GO was the active
material, carbon black was selected as the conductive additive and the binder was polyvinylidene
fluoride (PVDF). All the materials were weighed using a chemical balance and placed in a small
beaker. Then excessive amount of acetone and dimethylformamide (1:1 ratio) were added to the
beaker, covered with an aluminum foil and stirred for 12 hours. Mixture was poured on to a copper
foil pasted on a glass to form a very thin layer. It was allowed to dry. The electrodes were
fabricated by cutting the copper foil to required shape. A half-cell was assembled using the
fabricated GO anode with a gel electrolyte and sodium metal as the reference electrode.
Assembling and testing of the cell was conducted inside a N2 filled glove box. Discharging current
of the half-cell under 0.5 kΩ load over time was measured and it was recorded using a computer
interfaced program.
Description
Keywords
Mineral Sciences, Science and Technology, Mineral, Materials Sciences, Electronic Engineering, Graphite Industry